Field of the Invention
The present invention relates to a method for assembling a gas sensor including a ceramic sensor element and to an assembly apparatus for use in assembling the same.
Description of the Background Art
Conventionally, there have been well known gas sensors having sensor elements formed from an oxygen-ion conductive solid electrolyte ceramic, such as zirconia (ZrO2), as devices for determining the concentrations of predetermined gas components in measurement gas, such as combustion gasses and exhaust gasses in internal combustion engines such as automobile engines.
Such gas sensors generally include a sensor element (detection element) with an elongated plate shape which is made of a ceramic, wherein the sensor element is secured by a plurality of ceramic supporters which are ceramic insulators and by powder compacts made of ceramics such as talc which are embedded between the ceramic supporters, in a hollow portion of a metal housing and a cylindrical inner tube secured thereto through welding, so that the powder compacts provide hermetic sealing. There have been already well known methods and apparatuses for preferably assembling such gas sensors (refer to International Publication WO 2013/005491 and Japanese Patent Application Laid-Open No. 2005-37372).
International Publication WO 2013/005491 discloses a method which enables annularly-mounted members, which are the plural members to be annularly mounted on a sensor element, to be annularly mounted without fail even when the sensor element has warpage and, also, there is a smaller dimensional tolerance between the sensor element and the annularly-mounted members.
With the method disclosed in International Publication WO 2013/005491, the annularly-mounted members are annularly mounted to the sensor element, from its end portion provided with an opening portion for introducing measurement gas into the inside of the element. Therefore, if this method is applied to a sensor element which is covered with a protection film (protection layer) over the surface of this end-portion-side of the sensor element, this induces malfunctions such as injuries and exfoliations of the protection film, which is unpreferable.
On the other hand, Japanese Patent Application Laid-Open No. 2005-37372 discloses a method for fabricating a gas sensor including a detection element which is not covered with a protection layer at its one end portion. However, in the fabrication method disclosed in Japanese Patent Application Laid-Open No. 2005-37372, annularly-mounted members are temporarily annularly mounted to a pin member with a shape similar to that of the detection element and, thereafter, the pin member is pulled out therefrom to realize a state where the plural annularly-mounted members are stacked, and, then, the detection element is inserted into the stacked annularly-mounted members. This induces the problem that the annularly-mounted members are liable to displace, when the pin member is pulled out therefrom, and when the detection element is inserted thereinto.